Removing nitrogen compounds by oxidation



United States Patent 3,162,598 REMOVING NITROGEN COMPOUNDS BY OXIDATION Wayne L. Discgna, Markham, BL, assignor to Sinclair Research, Inc., Wilmington, Del., a corporation of Delaware N0 Drawing. Filed Mar. 12, 1962, Ser. No. 179,206 4 Claims. (Cl. 208254) The present invention relates to the removal of nitrogen contaminants from hydrocarbon feedstocks.

In recent years there has been an increased effort to improve hydrocarbon feedstocks by hydrotreating in the presence of catalyst. These hydrotreating operations include for instance, hydrodesulfurization, hydrocracking, isomerization, hydroforming, etc. Many of these hydrocarbon stocks are known to contain considerable quantitles of both sulfur and nitrogen in addition to the principal hydrocarbon constituents. It is known, however,

that the sulfur compounds contained in these stocks are detrimental .to precious metal catalysts, such as the platihum-type catalysts, but have little efiect on sulfur resist ant catalysts such as cobalt molybdate catalysts. Nitrogen compounds, on the other hand, have a definite adverse eifect on all catalysts, severely impairing their efficiency.

It has now been discovered that nitrogen compound containing hydrocarbon feedstocks can be materially reduced in nitrogen content by treating the feedstock with small but elfective concentrations of peroxychromate ions. Thus, the present invention provides a method for preparing a feedstock which on catalytic hydrotreating permits more complete utilization of the catalyst employed.

In accordance with the present invention the hydrocarbon feedstock contaminated with nitrogen compounds is intimately contacted with minor eflective amounts of peroxychromate ions usually in a concentration of about 0.1 to weight percent of the hydrocarbon feedstock and the resulting precipitate is removed. Since perchromates are normally unstable, it is preferred that the peroxychromate be provided in the petroleum stock in situ. This may be accomplished, for instance, by adding chromic acid and a concentrated aqueous solution of hydrogen peroxide in stoichiometric amounts, e.g., approximately equal amounts, to the contaminated hydrocarbon feedstock and stirring the mixture for a short period of time, usually at least about minutes.

The first reaction which occurs in this method is between chromic acid and hydrogen peroxide to form the peroxychromate ions and water. The peroxychromate ions then react with the nitrogen compounds in the hydro carbon feed to form a stable complex which precipitates out of the feed. Any excess peroxychromate formed decomposes to chromate which also precipitates out of the feed so that little if any chromium is left in the hydrocarbon stock to become a metal contaminant. The water formed settles as a layer and can be removed as by draining and the precipitate formed can be removed, for instance, by filtration. Generally the efiFective concentration of peroxychromate ion can be provided by employing about 0.1 to 10 weight percent of chromic acid and 0.1 to 10 Weight percent of concentrated aqueous hydrogen peroxide solution. These weight percents are based on the hydrocarbon feedstock.

In addition to concentrated aqueous hydrogen peroxide solutions, other oxidizing agents having an oxidation potential similar to that of hydrogen peroxide, that is, capable of forming peroxychromate ions on reaction with chromic acid, can be used. Also inorganic peroxides such as chromium peroxide and per salts such as perborates, persulfates, permanganates which in a slightly acidic environment form hydrogen peroxide, can be employed.

3,162,598 Patented Dec. 22, 1964 While the nitrogen-reducing method of the present invention can be carried out under normal conditions of temperature and pressures, slightly increased temperature can be used and may increase the rate of reaction and as a consequence reduce the time necessary to complete the precipitation. Generally temperatures of up to about 40 C. and preferably less than about 25 C. are employed. The lower temperature limit is that sufiicient to effect the reaction and is preferably at least about 20 C.

The feedstocks which can be subjected to the treating method of the present invention are liquid hydrocarbons derived from virtually any source which are contaminated with nitrogen compounds and include normally solid hydrocarbons which can be reduced in viscosity by adding light hydrocarbons such as aromatic solvents, mineral oil, etc. to them. Normally the hydrocarbon feed treated will have a nitrogen content of at least about 0.2 weight percent since these are the stocks that have the greatest adverse effects on hydrotreating catalysts. The nitrogen compound contaminants are usually naturally occurring in the feeds, e.g., mineral oils, in combined form, e.g., as organic compounds. The feedstocks of the present invention include for instance, hydrocarbons boiling primarily in the range of about 200-600 F. for instance, shale oil, coal tar, petroleum hydrocarbons such as residual oils, straight run and cracked distillates, for instance, naphthas, heavy gasoline fractions and gas oils.

The following examples are included to further illustrate the present invention:

EXAMPLE I A hydrocarbon feedstock boiling from about 460 to 480 F., primarily monomethyl naphthalenes, was fed to a reaction vessel and treated with 1.0% CrO and 1.0% of a 30% H 0 solution at room temperature and atmospheric pressure for thirty minutes with constant stirring. The water formed was drawn from the bottom of the vessel, and the resultant precipitate was filtered olf. The analyses of the feed and product are given in Table I.

A sample of petroleum vacuum asphalt bottoms was heated to 100 F. and dissolved in an equal volume of toluene. The mixture was then treated as mentioned in Example I. The toluene was then distilled oil. The analyses of the feed and product (average of 3 runs in the case of percent N removal) are given in Table II.

Table II Feed Product Percent Removal Percent O 85. 71 86. 02 Percent H 10. 26 10.53 Percent N .21 70 Percent S 3. 03 3. 00 P.p.m. NiO 83 68 18 P.p.m. V205 390 289 26 The data of Tables I and II demonstrate that the method of the present invention is capable of effectively removing from hydrocarbon feedstocks over 70% of the nitrogen compounds contained therein. Table II also shows that the method also removes vanadium and nickel contaminants from the feeds.

drq axb n f qd tqqk h ch ompr s ng hydr carbon feedstock containing nitrogen compound contarninants With about 0.1 to 10 weight percent chromic acid and 0.1 to 10 weight percent of a concentrated aqueous solution of hydrogen peroxide, said percentages being sufficient to provide effective concentrations of paroxychrornate ions and removing the resulting Water and precipitate.

References Cited in the file of this patent UNITED STATES! PATENTS 2,944,011 Murry- July 5', 1960 2,976,233 S elbin Mar. 21, 1961 3,016,349

Oswald et a1 Jan. 9, 1962 

1.A METHOD OF REDUCING THE NITROGEN CONTENT OF HYDROCARBON FEEDSTOCKS WHICH COMPRISES INTIMATELY CONTACTING A LIQUID HYDROCARBON FEEDSTOCK CONTAINING NITROGEN CONTAMINANTS WITH A MINOR, EFFECTIVE CONCENTRATION OF PEROXYCHROMATE IONS AND SEPARATING THE PRECIPITATE FORMED. 